1. Field of the Invention
The present invention relates to an apparatus that controls capacitor discharge.
2. Description of the Related Art
In an image forming apparatus as an example of an apparatus including a substrate equipped with a capacitor, when the substrate is inserted or withdrawn for the purpose of maintenance, the substrate to be inserted or withdrawn needs to be prevented from being destroyed due to a hot swap caused by electric charge charged to the capacitor. To this end, some methods are discussed relating to the discharge of the capacitor.
For example, Japanese Patent Application Laid-Open No. 61-032400 discusses a flash lamp for emitting light by discharge of electric charge charged to a capacitor, a power-off detection circuit for detecting that a power source is turned off, and a power source for the flash lamp that causes the capacitor to forcibly discharge when the power-off state is detected.
Japanese Patent Application Laid-Open No. 07-333751 discusses an image forming apparatus including a protective cover and an emergency discharge circuit including a switch for detecting an installed condition of the protective cover, wherein, when removal of the cover is detected, electric charge stored in the capacitor is discharged.
Recently, power-saving has been promoted more and more. For example, a printer that performs a standby operation with a standby power of 1.0 W is discussed. The printer capable of performing the standby operation with such low power consumption is provided with an all-all-night power source. The all-night power source is provided, for example, for detecting an access to the printer from the external device even when a power source of the apparatus main body is set to an OFF state by a user operation. Accordingly, the power source of the printer can be automatically returned from the OFF state at any time the user desires to use the printer.
The all-night power source is described below in more detail. The all-night power source is normally equipped with a capacitor in order to generate a smoothed power source output and performs the above described standby operation while continuously charging the capacitor (i.e., while storing electric charge to the capacitor). For example, in a case where the image forming apparatus is placed in the standby state with low power consumption such as 1.0 W, it is desirable that the power to be consumed in charging the capacitor is minimized as much as possible. In this regard, to minimize discharge of the capacitor as much as possible, a measure for interrupting the discharge path is provided in the circuit. This is because, if a large current is discharged, the circuit operates to charge the corresponding amount of current, resulting in inviting an increase of the standby power.
As described above, not only the low power consumption of the printer in the standby operation but also improved usability, e.g., automatic return of the printer from the standby operation, has been also required lately. To the contrary, in the method that the electric charge of the capacitor is automatically and immediately discharged as it is discussed in Japanese Patent Application Laid-Open No. 61-032400 and Japanese Patent Application Laid-Open No. 07-333751, easier maintenance can be realized but the improved usability cannot be realized to a satisfactory level.
On the other hand, as described above, when the substrate is inserted or withdrawn for the purpose of maintenance, to prevent the substrate to be inserted or withdrawn from being destroyed due to the hot swap caused by the electric charge charged to the capacitor, it is necessary to discharge the capacitor. However, in the printer equipped with the all-night power source including the above described capacitor, the electric charge of the capacitor cannot be discharged immediately and automatically. Therefore, a service person is forced to wait for completion of the discharge of the electric charge of the capacitor for a long time.
A solution for the above issue can be found in providing the printer with a circuit that can detect disconnection of a power source cable from an alternating current (AC) inlet and can change the capacitor to automatic discharge of the electric charge. However, the above solution requires a new automatic detection circuit for detecting the disconnection of the power source cable from the AC inlet. As a result thereof, the solution invites an increased cost. For example, while the printer is in a standby state with the standby power of 1.0 W, it is necessary to operate the automatic detection circuit using a zero crossing detection. Accordingly, an operation power to be used in a photocoupler or the like increases. Alternatively, in order to save data in a case of power outage or power shutoff, a configuration can be assumed that reads and writes a memory by using the electric charge charged to the capacitor. However, in the case of the above assumption, if the electric charge of the capacitor is discharged immediately in a manner as discussed in Japanese Patent Application Laid-Open No. 61-032400 and Japanese Patent Application Laid-Open No. 07-333751, a possible problem is created in an operation of the printer.
Such a problem is created not only for the image forming apparatus as described in the above example but is commonly created to all the apparatus equipped with the capacitor.